The invention relates to a device for operating a tool, such as a core drilling device or a grinding device with an ultrasound adapter, for example, for the abrasive or metal cutting processing of solids, such as building materials, for example, rock, metal or wood.
The abrasive sawing processing of rock by means of a cylindrical cutter or drill bit, edged with hard materials on its leading end, is known, for example, from EPO280835. Such cutters or drill bits usually employ water as a flushing and cooling liquid. The ultrasonic vibrations are formed by capacitive, electro-acoustic transducers in the ultrasonic frequency range. The electrostatic transducer may be constructed, for example, from pre-tensioned piezo disks.
Capacitive electro-acoustic transducers in the ultrasonic frequency range, such as piezo disks, consist of an electrostrictive material as the dielectric of a capacitor, which changes its dimensions under an applied electrical voltage. Because of its mechanical properties, a capacitor of such construction has an intrinsic resonance. To produce sufficient deformations, capacitive electro-acoustic transducers require a high electric voltage.
It is customary to supplement electric (capacitive) behavior of a piezo electric transducer by an inductivity, which is tuned so that the resulting parallel oscillating circuit on the electrical side has the same resonance frequency as the mechanical oscillating circuit, which is determined by the stiffness and mass of the sound converter.
According to the EP0720890B1, a hand device for operating a tool has a rotating, cylindrical, abrasive, material-removing tool, on which a longitudinal ultrasonic field is superimposed axially over a capacitive electro-acoustic transducer consisting of an electrostrictive material. Corresponding to the resonance, the cutter or drill head is designed for the frequency of the ultrasonic field.
According to the U.S. Pat. No. 3,614,484, an ultrasonic adapter for a drill driving a rotating tool, has a capacitive electro-acoustic transducer, which rotates along with the drill, consists of an electrostrictive material and is connected over slip rings with an ac voltage of ultrasonic frequency. The wear, which is caused by mechanical contact and limits the service life, is a disadvantage of such an energy supply. Moreover, due to the use of water and taking into consideration the high voltage required to operate electrostrictive transducers, insulation problems arise, which can affect the safety of the user.
Moreover, according to EP0680060A1, annular, rotatable rotation translators or transformers with, in each case, circular U-shaped parts for stator and rotor are known. Over assigned coils, they transfer electrical energy over an alternating magnetic field from the stator to the rotor.
It is an object of the invention to avoid the above disadvantages in the realization of a device for operating a tool including an ultrasonic adapter for impressing an ultrasonic oscillation on the tool. A further aspect involves superimposing an ultrasonic oscillation on the rotational movement of the tool.
Essentially, for the contactless transfer of energy, the ultrasonic adapter of a tool device has a capacitive electro-acoustic transducer connected with the secondary winding of a transformer, the primary winding of which is connected with an electrical ultrasonic frequency generator, which produces an ac voltage in the ultrasonic range and accordingly, over the alternating magnetic field, transfers the electrical power contactless to the capacitive electro-acoustic transducer. At the same time, in conjunction with the capacitive electro-acoustic transducer, the secondary winding forms a parallel resonance circuit and, in the resonance case, brings about a voltage overshoot.
The mechanical wear, which is reduced significantly by the contactless transfer of energy, has an advantageous effect on the service life of the device. Moreover, working with water-contaminated materials does not result in any insulation problems during the transfer of energy. By using the secondary winding as parallel inductance, additional inductance is not required for balancing the oscillating electric circuit.
Advantageously, in the case of a possible, yet not necessary movement of the tool, rotating or swinging at least partially about a tool axis, a capacitive electro-acoustic transducer, rotating or swinging along at least partially with the tool, is connected contactlessly over a transformer, which can rotate at least partially, with the ultrasonic frequency generator.
Furthermore, the resonance frequencies of the capacitive electro-acoustic transducer, of the secondary oscillating circuit, of the primary oscillating circuit as well as of the amplitude of the longitudinal oscillations of the tool, especially of a cutter or drill bit, are tuned, to the frequency of the ultrasonic frequency generator.
Preferably, a partial component of the transformer of the contactless energy transfer, for example, the secondary winding, can be used to tune the electrical resonance circuit with the capacitive electro-acoustic transducer.
Moreover, the mass of a partial component of the transformer of the contactless energy transfer, such as the mass of the inner transformer core, can be used for tuning the mechanical resonance circuit of the tool.
Due to the above multiple utilization of partial components of the transformer of the contactless transfer of energy, in conjunction with a radial, nested arrangement of the partial components, such as, from the inside to the outside, of the inner transformer core, the secondary winding, the air gap, the primary winding, the outer transformer core, a largely compact construction can be realized advantageously for the transformer of the contactless transfer of energy.
Advantageously the transformer is formed from two coils within two U-shaped pot cores, the openings of which face one another and which together accordingly form an essentially closed pot core, a coil being assigned nonrotationally to each U-shaped pot core.
Alternatively, the rotatable transformer consists of two U-shaped pot cores, which are nested together, oriented oppositely with respect to the tool axis and contain in each case nonrotationally assigned coils, which are oriented parallel to the tool axis, the primary winding being assigned as the stator, which is connected nonrotationally with the device, and the secondary winding being assigned as the rotor, which is connected nonrotationally with the tool.
Furthermore another advantage, with respect to a diameter, an inner U-shaped pot core and the secondary coil are in the radial interior and an outer U-shaped pot core and the primary coil are in the radial exterior. As a result, there is one degree of freedom of motion parallel to the tool axis, alongside of which a decoupling of the oscillation as well as a dismantling of the transformer, for example, when changing a tool with an integrative capacitive, electro-acoustic transducer and a secondary part of a transformer, becomes possible.
In order to minimize the overall size of she transformer, a winding ratio of 1:1 is advantageous. The small number of windings furthermore results from a supply frequency in the range of 20 to 35 kHz.
The mass of the ferromagnetic, inner transformer core acts as an oscillating mass and can be used to balance the oscillating mechanical system.
Preferably, this internal transformer core is built up from stratified lamellas, which are insulated electrically from one another. In order to avoid eddy current losses, the lamellas follow the magnetic lines of field and are assembled piece-by-piece or shaped by non-cutting procedures.
Furthermore, the capacitive electro-acoustic transducer advantageously is disposed along the tool axis, so that the vibrational amplitude, occurring in the direction of the tool axis, increases the abrasive removal of material by local axial pressure magnification.
Advantageously with respect to the amplitude of the longitudinal oscillations of the tool, the capacitive electro-acoustic transducer is disposed at a vibration node.